Esprit2 wrote: qwerty wrote:Thickness of the Gates Blue T104RB excluding tooth height is averaging 2.35 - 2.40mm measuread at various points around the belt and on both sides. I will be able to measure a Gates HSN and JHPS belt tomorrow.Did you ever measure the Gates HSN & JPS belts? I just measured a new Flennor 24513311 black belt, and two other used belts I couldn't identify, and the readings were all 0.088-0.089 inch (2.235-2.261 mm). That's about 0.004" / 0.1mm difference between the blue & black belts. Not as much as between the blue & black HTD belts.

Stretching my memory, but for the HTD belts, I think the difference was more like 0.016-0.015"), and that made about a 3-5 lb difference in Burroughs readings.
JHPS Belt Gates T104 White writing - 2.40mm - 2.45mm
Gates Green T104 HTN Belt - 2.50mm +0.00 -0.00
Gates Green T104 HTN Belt - 2.40mm - 2.45mm
Gates T104RB Blue Belt 2.20 - 2.30mm (I ordered two belts this is the second one, the first is measured above with different verniers).

The above all measured with the same verniers in the same way, so could account for the discrepancy. The blue belt was +- 0.05 around the belt with tolerance whereas the black belts were pretty uniform. Interestingly the two green HTN Belts measured differently with ~0.1mm difference.

This little thingy has become an invaluable tool while troubleshooting the timing belt so i'll elaborate. It looks like lot of steps but it's really not, just being clear.

Cut a length of used belt to 215mm cut on an angle (Pic Attached) I started from the inside of one tooth to the outer of two teeth over. The pic will explain (Blue Line)

Turn inside out and Temporarily super glue with the teeth aligned, the teeth need to be pretty accurately aligned.

Align cam gears to exactly TDC, we need to get this spot on as installing the tool and additionally while it's in place installing a belt will be a lot easier later on

After glue has completely dried push into cam gears, you should have two empty circles at either end

Insert top and bottom hard circular fillers (Aluminium) in my case, anything hard can be used, we just want to stop rotation. Mine was 15.3mm and 18.0mm yet an average will most likely work of 16.65mm each. Just as long as they are snug and all the teeth sit nicely.

Once the hard circular fillers are in there, partially fill with Sikaflex to bond the shape, make sure you get a fix on both the top and bottom surfaces as we want to keep it's shape when we remove it. Leave overnight but don't let it seep out the back of the belt and on to the cam sprockets.

Once dry Remove it, then reinsert making sure it fits and it's kept it's shape. If it doesn't reinsert and fill a bit more making sure not to soil the cam sprockets.

Once you have a nice fit take it to a dry flat surface and fill all of it, i cut an additional piece of belt as a backing, traced it and pushed it in and filled it solid, we don't any want rotation.

I then ground a lead in with a linisher to make it easier to insert and also marked the center TDC tooth for reference.

In use it takes a good thumb push to get it in there but once it's in it instils confidence.

The trapezoidal tooth belt is standard for the JH 907. If your engine has the round-tooth HTD pulleys, then that was a very worthwhile upgrade you or some prior owner made to the engine.

A bunch of years ago, JAE worked with Gates Racing to have the blue HTD belt produced in the Lotus size. Since JAE paid for the development, it's an exclusive to them and Gates does not sell it over-the-counter. In turn, JAE sells it to other Lotus specialists, and to Lotus Cars itself. So while you might find blue HTD belts at several Lotus specialists, ultimately they all come from JAE. There is no standard Gates part number that will get you a blue HTD belt at your local auto parts store or motor factor.

I was PM'd and asked for a similar Burroughs/ Krikit spec for the black trapezoidal tooth belt. I thought others might find the info useful, so here's what I replied:

*~*~*~*

With the Burroughs BT-33-86J or the BT-33-73F, set a new black trapezoidal tooth belt's tension a little high, at 100 (55 Krikit KR-1), to allow for initial stretch. After 500-1000 miles, the belt will have taken an initial stretch, and the tension will end up about where it's supposed to be for normal running... around 95

Then for routine checking and re-tensioning of a used belt, set the tension to the normal running spec of 95 Burroughs (52.25 Krikit). Lotus experimented through the years, started at 90 (too low), went as high as 105 (too high), and eventually settled at 95. It's a good tension value with a proven track record.

Neither gauge has great resolution, so the two-place decimal is just a matter of doing the math. Don't worry about trying to get anything closer than a round number... plus or minus. Personally, I'd rather err a little on the plus side. Anything over 105 Burroughs (58 Krikit) will cause a black belt to whine, and any belt that whines is too tight.

When you do a routine tension check, anything down to 90 Burroughs (49.5 Krikit KR-1) is acceptable. 90 is not "good", and 95 is better... but it's not "bad". Any lower than 90, and you should re-tension the belt as soon as possible.

The values given above apply to both the black HTD round tooth belt and the black trapezoidal tooth belt. The trapezoidal belt is supposed to run with more tension than the HTD belt. However, the Burroughs gauge is thickness sensitive, and the HTD belt is thicker than the trapezoidal belt. The end result is that the trapezoidal belt ends up tensioned as the Burroughs gauge says it is (95), and the HTD belt ends up a few pounds lower... where it should be. It works without the need to calibrate another gauge, and it's easier to remember one tension spec for both black belts.

The blue Gates Racing belts are another story. The tension for the blue HTD belt was discussed previously, and that's been worked out through owner experience over on the TurboEsprit list on YahooGroups. There is no offical factory tension spec for the blue HTD from either Gates or Lotus. This is all grassroots.

The blue trapezoidal belt is relatively new on the market, and I'm not aware of an established tension yet. Expect it to be a few pounds lower than the standard black trapezoidal belt tension. For starters, we're setting the tension just below (~comfortably below) the "whine threshhold". Sorry, I don't have an established number for you yet. If you use a blue trapezoidal belt, report your results so we can all learn from your experience. We'll add it to the collective experience/ knowledge base.

*~*~*~*

IMHO, the tension spec given in the JH Workshop Manual is too low. Finding a Kent-Moore KM-128 gauge might be difficult enough to keep anyone from using that tension spec, but the tension that results is too low. I won't recommend using it.

Using the Burroughs/Krikit comparison data I found either on this forum or perhaps a Lotus forum for the Gates T104 and also the recommended Burroughs values for the T104RB I calculated an approx 55% difference between the two gauges (cold) and installed my blue belt last week at 47 lbs cold. Belt deflections are in accordance with a Judson Manning post from 2006
(http://www.jensenhealey.com/forums/view_topic.php?id=528&forum_id=2&jump_to=3319
So far so good but I’ll be keeping my eye on it.

Rick,
Save yourself some grief, and don't set the tension hot. Always check or set the belt tension on a cold engine, before the engine has been started for the first time that day.

And don't use a twist test or belt deflections if you have access to a good gauge. Deflection tests are especially un-reliable since the different evolutions of the belt have different thicknesses and strength/ stiffness. They don't all react the same to a deflection load.

I did set the tension cold @ 47# with a Krikit. I included calculated hot specs only because they had been included in the T104 tension specs. The twisting & deflection test comparisons were done to reinforce that I was in the ballpark. I am open to more hands-on experience and recommendations but since none had been offered to this point I wanted to share mine.

Rick in Miami wrote:I did set the tension cold @ 47# with a Krikit.
Okay, good. I'm with you there.

Rick in Miami wrote:I included calculated hot specs only because they had been included in the T104 tension specs.
My concern was that it sounds to me like you're giving the hot tension too much credibility as a "Spec". It's not. There is no hot spec in terms of something with real value/ worth. If you properly set the tension cold, then allow the engine to warm up fully and measure the tension again, the hot tension you get is the result of your good procedure. In a cause and effect relation ship, hot tension is the effect, not the cause. Doing the correct procedure well, then gaining confidence in your work because it produced the "correct" hot result is bogus thinking. You're giving credibility to the hot result like it's the god given end goal. It's not. And it's not reliable. Purge if from your thinking as "something to attain".

What you're stating is like taking poison after the fact in order to bolster your confidence that you took the right blood pressure medicine this morning. There's something wrong with that.

Rick in Miami wrote:The twisting & deflection test comparisons were done to reinforce that I was in the ballpark.
Again, that's backwards. The twist & deflection test are not foundational. They're grassroots tricks that 'might' give ball park results if performed by someone with a practiced feel; but for an untrained first timer, the results are unreliable. The gauge measurement reinforces that you might have developed a practiced feel for the twist test... and frankly, I discount the deflection test as stated. But neither the twist nor deflection tests should be considered standards of correctness for any gauge.

Also, the twist and deflection test results vary dramatically with the stiffness of the belt. And the Gates Racing blue T104RB is thicker, and significantly stiffer than the old, black, HCR trapezoidal tooth belt. Twist test results for the blue belt (once they're developed) will be considerably different from those for the black belt. Don't mix them up.

Rick in Miami wrote:I am open to more hands-on experience and recommendations but since none had been offered to this point I wanted to share mine.
Thanks for sharing the results of what you're doing, and please don't get the feeling that I'm beating you about the head and shoulders. We do need to collect that sort of data to zero in on a good tension setting for the T104RB blue belt, and I appreciate your contribution. I'm just trying to curb the spread of some common mis-information along the way.

If you, or anyone, have the time and the inclination, it would also be helpful to know what happens as the tension is increased in small steps. At what initial cold tension does the belt begin to whine when the engine gets hot? And at what cold tension does the belt begin to whine right away... cold? Those are upper limits we need to avoid, but yet approach. Staying too low just out of fear of reaching an unknown whine threshhold isn't good... too low tension is hazardous. But how high can we go without provoking a whine. So far, I've not read of anyone sneaking up on those tension values for the T104RB. At least not in a statistically meaningful sample... more than one incidence. Much of that work has been done for the round-tooth HTD blue belt. And the recommended Burroughs tension for the blue HTD is in that 82-84 cold range (I use 83-84, but that's splitting hairs).

In your previous message, you wrote that you used the Burroughs/ Krikit conversion factor of 55%, and the recommended Burroughs values "FOR THE T104RB" to get to a target setting of 47 lbs cold. Where did you find the recommended Burroughs setting for the T104RB? The value you used matches what many are using for the round-tooth HTD blue belt. It would be convenient if the same value also turned out to be the best tension to use for the blue trapezoidal T104RB as well, but I haven't heard any definitive results that support that. I'm not contesting that tension for the T104RB. It's just that if there's more information on that posted somewhere, I'd really like to read it and learn. Point me to it.

The trapezoidal belt's shallow tooth engagement requires higher tension to maintain a secure bite on the pulley, and to not jump timing. The HTD belt's deeper tooth has a better mechanical bite, and can run with lower tension. I previously mentioned that the Burroughs gauge is thickness sensitive, and the round-tooth HTD belt is thicker than the trapezoidal tooth belt. With that in mind, Lotus recommends 95 on the Burroughs for both belts, and the thickness differences result is a lower actual tension in the HTD belt than in the trapezoidal belt.

Maybe that's what we'll confirm for the blue belts as well. If 82-84 Burroughs works well for the blue HTD, then perhaps it will also provide the adequately higher tension for the blue trapezoidal belt by virtue of it's thinner section producing a higher Burroughs reading.

The paranoid concern is that the tension is lower... 82-84 vs 95. And historically, low tension has not worked well for trapezoidal belts. The trapezoidal belt has a long, early history of jumped timing and bent valves. It has long been shown that the trapezoidal black belt needs all the tension it can get, short of provoking a whine, so there's some fear/ reluctance at work in the search for a new 'lower' tension for the blue T104RB. How low is too low?

Myself, I'd rather start high, discover the belt whines when hot, and work my way down to a lower setting that doesn't provoke a whine. I'm fearful of just blindly dialing in a quiet low tension, then waiting to see if it jumps timing down the road. Unfortunately, each trial requires letting the engine cool down over night, so only one trial per day will drag out any testing. And it would be nice to test a number of belts on a number of engines. One is not statistically meaningful.

Technically, the blue belt is a worthwhile improvement. We just need to learn how to use it without bending anyone's valves in the process. Hot tension, twist, and deflection tests are not safe ways to get there. 'Maybe' we back into blue belt versions of the hot, twist & deflection "specs" later, after we've first determined a viable cold tension by using good gauges.

I don't mean to just stand on the sidelines and point. But I have an unheated garage, and for now it's still cold here in Minnesota. Plus, the engines I have access to right now have HTD belts & pulleys. I'll jump into the game as soon as I can.

Thanks Tim – Advice well taken. I will try tightening further in increments (starting at the high end to introduce the whine) next week and share my findings. As for the Burroughs T104RB tension, I apparently misread a post on a Lotus forum discussing both the T104RB and the Blue HTD.

I finally got to play with the belt tension yesterday. I started by tightening the tensioner counter-clockwise to a tension that caused a whine when hot. Then I backed it off until there was no whine. After turning the cold engine over by hand several times this AM I got consistent Krikit readings of just barely above & barely below 50. I continued to turn the engine to 6-7 different positions testing several times at each position and got the same readings.

Good information, thanks for sharing. It's that kind of input that will help zero in on a preferred tension recommendation.

The tension varies with crank position. I've checked the tension in 10 degree increments for two full revolutions (ie, a 4-stroke cycle), and the graph of the results is a regular roller coaster ride. So it's important to check and set the tension at TDC. Explore if you wish, but set it using a tension gauge at TDC.

Around 1997 or so, Lotus issued a new procedure for the HTD round tooth belt only. It called for the use of a Clavis Frequency Meter to set the tension to 100-110 Hz at 30 BTDC. I find it much easier to set the crank to 30 BTDC than to TDC. The tension in the belt is higher at TDC, so it's more difficult to move it precisely, and it moves in jerks. If you're right next to the TDC mark trying to sneak up on it, pulling... pulling... then it jerks beyond TDC. Frustrating.

At 30 BTDC, it's easier to turn the crank, and you can roll right up to the TDC mark and stop, first time, every time. The only problem, there's no tension recommendation for the trapezoidal belt at 30 BTDC. That would be another grassroots effort.

So, out of curiosity, what tension are you zeroing in on at TDC? Then what is the corresponding tension at 30 BTDC? Curious minds want to know. Well, at least one does.

BTW, one of the nice things about the frequency method is that there are inexpensive/ free guitar tuning aps for smart phones, and even frequency analyzers. TuneIt! is one. With that installed, you can simply hold your phone or iPad down by the belt, and pluck it like a guitar string. The frequency appears on the screen.